In multi-chamber pacing of a heart, an implanted medical device such as a pacemaker delivers pacing pulses to two or more chambers of the heart. The timing of the pacing pulses is important. Many patients benefit from having chambers paced in a particular order with a delay between the respective pacing pulses.
A patient who has undergone an ablate and pace therapy presents an example of a patient that may benefit from the timing of multi-chamber pacing pulses. Ablate and pace therapy is often used with patients having symptomatic drug-refractory atrial fibrillation. In many patients, ablate and pace therapy has been found to reduce the frequency of atrial fibrillation conducted to the ventricle and improve the quality of life. Ablate and pace therapy includes a surgical procedure in which a surgeon surgically ablates the atrioventricular junction of the heart and implants a pacing system. The implanted pacing system supplants, to some extent, the heart's natural pacing system.
The dual-chamber pacing system includes a right ventricular pacing lead positioned conventionally in the right ventricle of the heart and a left ventricular pacing lead positioned via the coronary sinus in a cardiac vein, such as the middle or great cardiac vein. The pacing leads include electrodes that sense electrical activity. These “senses” may be indicative of cardiac activity such as ventricular contraction. The pacing electrodes also supply paces to the heart, i.e., electrical impulses generated by the implanted pacemaker that cause the heart to contract.
The right ventricular (RV) pace/sense electrode can deliver paces to the right ventricle and the left ventricular (LV) pace/sense electrode deliver paces to the left ventricle. Although the paces to the ventricles may be delivered simultaneously, patients may benefit from having one ventricle paced before the other.
On some occasions, the ventricles may contract intrinsically, i.e., in response to an activation generated by the heart instead of by the pacemaker. The pacing system senses intrinsic contractions via the RV and LV pace/sense electrodes.
Some senses may not be valid. Senses via the LV pace/sense electrode, in particular, are susceptible to being invalid. In other words, the LV pace/sense electrode is susceptible to detection of signals that may be mistaken by the pacemaker for the electrical signals that accompany a ventricular contraction. An invalid sense may be caused by a far field P-wave, i.e., the electrical activity of the atria sensed by a ventricular lead. Another invalid sense may be caused by myopotentials, i.e., electrical signals from muscles other than the heart. These senses are invalid because they accompany activity other than ventricular activity.
In some forms of cardiac therapy, the pacemaker applies therapy in response to sensed cardiac activity. Such therapies may depend upon the ability of the pacemaker to receive valid senses. If some or all of the senses are invalid and the pacemaker cannot discriminate between valid and invalid senses, the pacemaker may apply therapy that is not needed, or may apply needed therapy inappropriately.
Multiple-chamber pacing systems are known in the art, including systems that pace and sense the right ventricle and the left ventricle. In addition, techniques associated with cardiac tissue ablation are known in the art, as are techniques for generating pulses to block orthodromic pulses. Examples of these techniques and/or devices may be found in the issued U.S. Patents listed in Table 1 below.
TABLE 1U.S. Pat. No.InventorIssue Date6,088,614SwansonJul. 11, 20006,081,748Struble et al.Jun. 27, 20006,070,101Struble et al.May 30, 20005,944,743JanssensAug. 31, 19994,928,688MowerMay 29, 19904,608,985Crish et al.Sep. 02, 1986
All patents listed in Table 1 above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments and claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the techniques of the present invention.